This invention relates to an enhancement of the DALI protocol, additionally enabling the manual control of digital ballasts in a lighting control network, and a DALI compliant communications apparatus to interpret the enhanced protocol. The invention has particular application in a lighting control network compliant with the Digital Addressable Lighting Interface (DALI) standard.
The DALI protocol is a method whereby electronic ballasts, controllers and sensors belonging to the system in a lighting network are controlled via digital signals. Each system component has its own device-specific address, and this makes it possible to implement individual device control from a central computer.
Research work connected to the DALI project began midway through the 1990s. However, the development of commercial applications got underway a little later, in the summer of 1998. At that time, DALI went under the name DBI (Digital Ballast Interface). An interface device (or ballast) is an electronic inductor enabling control of fluorescent lamps. The DALI standard has been the subject of RandD by numerous European ballast manufacturers such as Helvar, Hxc3xcco, Philips, Osram, Tridonic, Trilux and Vossloh-Schwabe. The DALI standard is understood to have been added to the European electronic ballast standard xe2x80x9cEN60929 Annex Exe2x80x9d, and was first described in a draft amendment to International Electrotechnical Commission 929 (xe2x80x9cIEC929xe2x80x9d) entitled xe2x80x9cControl by Digital Signals.xe2x80x9d DALI is thus well known to those skilled in the art. Due to this standardization, different manufacturers"" products can be interconnected provided that the manufacturers adhere to the DALI standard. The standard embodies individual ballast addressability, i.e. ballasts can be controlled individually when necessary. To date, ballasts connected to an analog 1-10 V DC low-voltage control bus have been subject to simultaneous control. Another advantage enabled by the DALI standard is the communication of the status of ballasts back to the lighting network""s central control unit. This is especially useful in extensive installations where the light fixtures are widely distributed. The execution of commands compliant with the DALI standard and obtaining the status data presupposes intelligence on part of the ballast. This is generally provided by mounting a microprocessor within a DALI compliant ballast; the microprocessor also carries out other control tasks. Alternatively, two microprocessors can be utilized; one to interpret and service the DALI communications, and the other to provide the lamp control and diagnostics. The first products based upon the DALI technology became commercially available at the end of 1999.
The word xe2x80x98digitalxe2x80x99 is a term which has become familiar to us all in the course of this decade in connection with the control technology built into domestic appliances as well as into industrial processes. Now, digital control is becoming increasingly common in the lighting industry as a result of the new DALI standard.
DALI messages comply with the Bi-Phase, or Manchester, coding scheme, in which the bit values xe2x80x981xe2x80x99 and xe2x80x980xe2x80x99 are each presented as two different voltage levels so that the change-over from the logic level xe2x80x98LOWxe2x80x99 to xe2x80x98HIGHxe2x80x99 (i.e., a rising pulse) corresponds to bit value xe2x80x981xe2x80x99, and the change-over from the logic level xe2x80x98HIGHxe2x80x99 to xe2x80x98LOWxe2x80x99 (i.e., a falling pulse) corresponds to the bit value xe2x80x980xe2x80x99. The coding scheme includes error detection and enables power supply to the control units even when there are no messages being transmitted or when the same bit value is repeated several times in succession. The bus""s forward frame (used in communications from the central control unit to the local ballast) is comprised of 1 START bit, 8 address bits, 8 data/command bits, and 2 STOP bits, for a total of 19 bits. The backward frame (from the local ballast back to the central control unit) is comprised of 1 START bit, 8 data bits and 2 STOP bits, for a total of 11 bits. The specified baud rate is 2400.
DALI messages consist of an address part and a command part. The address part determines which DALI module the message is intended for. All the modules execute commands with xe2x80x98broadcastxe2x80x99 addresses. Sixty-four unique addresses are available plus sixteen group addresses. A particular module can belong to more than one group at one time.
The light level is defined in DALI messages using an 8-bit number, resulting in 128 total lighting levels. The value xe2x80x980xe2x80x99 (zero), i.e., binary 0000 0000, means that the lamp is not lit. The remaining 127 levels correspond to the various dimming levels available. The DALI standard determines the light levels so that they comply with the logarithmic regulation curve in which case the human eye observes that the light changes in a linear fashion. All DALI ballasts and controllers adhere to the same logarithmic curve irrespective of their absolute minimum level. The DALI standard determines the light levels over a range of 0.1% to 100%. Level 1 in the DALI standard, i.e., binary 0000 0001, corresponds to a light level of 0.1%.
Go to light level xx.
Go to minimum level.
Set value xx as regulation speed.
Go to level compliant with situation xx.
Turn lamp off.
Query: What light level are you on?
Query: What is your status?
The idea concerning the DALI protocol emerged when the leading manufacturers of ballasts for fluorescent lamps collaborated in the development of a protocol with the leading principle of bringing the advantages of digital control to be within the reach of as many users as possible. Furthermore, the purpose was to support the idea of xe2x80x98open architecturexe2x80x99 so that any manufacturer""s devices could be interconnected in a system.
In addition to control, the digital protocol enables feedback information to be obtained from the lighting fixture as to its adjustment level and the condition of the lamp and its ballast.
Examples of typical applications for systems using the DALI protocol are office and conference facilities, classrooms and facilities requiring flexibility in lighting adjustment. The lighting-control segment based on the DALI technology consists of maximum 64 individual addresses which are interconnected by a paired cable. DALI technology enables cost-effective implementation of lighting control of both smart individual lighting fixtures as well as of numerous segments connected to the automation bus of a building.
Because the DALI standard assumes that the local electronic ballast will be continually under the control of the central computer controlling the network or the series of networks (recall that under the DALI standard 64 unique addresses are available, but by setting one or more of these unique addresses to be assigned to another network chaining of networks can result and numerous individual luminaries can be controlled) there is no facility in DALI for temporarily taking a particular ballast xe2x80x9coff linexe2x80x9d and subjecting it to purely manual control, and then setting it back xe2x80x9con line.xe2x80x9d As a result, under the current state of the art, in order to allow for the manual control of a local electronic ballast by the occupant of the room or office in which that ballast exists, some additional circuitry or wiring would be required to somehow cause the manual suspension of commands coming from the lighting network for an interval of time. Such additional circuitry or wiring would be in addition to the existing circuitry in the electronic ballast increasing the cost of the ballast and its complexity. Alternatively, additional circuitry and wiring could be provided to control the ballast by DC control or by a pulse width modulation, but this option would also increase the cost and complexity. What is desired is a protocol which would enhance the DALI standard, and would be easily decodable by DALI compliant ballasts without the addition of additional circuitry or pins, or a change in the signal type (such as to DC or pulse modulated) so as to allow for the suspension of the network commands for an interval of time to afford the human occupant of the room or space in the building in which the electronic ballast and the luminary is located to manually set the dimming level or turn off the lamp.
Additionally, the current state of the art provides the intelligence to the ballast required by the DALI standard by means of a microprocessor. However, the lamp control and diagnosis in an electronic ballast also must be controlled by a microprocessor. As described above, for maximum availability of the microcontroller to handle lamp control and diagnostics, two microprocessors per ballast are required. Alternatively, one microprocessor could be used, and it would have to service both the DALI communications traffic as well as control the lamp. This latter solution is more efficient, at the price of an additional microprocessor. What would be truly desirable is a separate ASIC dedicated to handle the DALI communications and messaging.
The above-described problems of the prior art are overcome in accordance with the teachings of the present invention which relates to an enhanced protocol for enabling manual control of electronic ballasts in lighting control networks which are compliant with the DALI standard, as well as the design of a communications apparatus for decoding both standard DALI messages, as well as local manual control messages. As described below, the signaling is arranged such that certain signal lengths below a predetermined threshold are interpreted as DALI commands, and lengths above a threshold are interpreted as manual overrides. Moreover, the control information in the manual override signal is also conveyed by measuring the length of such signal. In a preferred embodiment the lamp is controlled by a microcontroller, and the DALI commands are interpreted by a specialized processor.